I've said all along that the key to any revival of Downtown hinges upon the energy efficiency of it's buildings. Here's a great example of retrofitting a sky scraper for energy eficiency, the Empire State building.

http://www.popsci.com/science/articl...nic-skyscraper

Image gallery of the window retrofits:
http://www.popsci.com/technology/gal...ate-goes-green